Scientific abstract Genome-wide association studies have provided >230 genetic variants associated with susceptibility to multiple sclerosis (MS). The theme emerging from these studies is that MS risk variants perturb gene regulation in activated lymphocytes, supporting the view that MS is mediated through dysregulation of lymphocytes. Absent from this picture is a role for glial cells, despite substantial evidence that these cells are critical players in MS lesion formation. In this proposal, we are challenging the lymphocyte-centric view of genetic MS susceptibility. We hypothesize that genetic variants mediate MS risk in part by dysregulating astrocyte function. Since NF-?B signaling is a central pathway in MS pathology, we will determine the impact of two common NF-?B relevant risk variants, rs1800693G (intronic to TNFRSF1A) and rs7665090G (proximal to NFKB1), on inflammatory response in astrocytes. This will be examined in human astrocyte cultures, derived from genome-edited induced pluripotent stem cells (aim 1), and in reactive astrocytes within active MS lesions (aim 2) with the risk and protective genotypes. In addition, we will quantify variant-driven changes in the lesion environment such as lymphocyte infiltration, lesion size, cellular phenotypes and phenotype interactions. In aim 3, we will systematically identify the MS risk variants that are active in astrocytes and the genes that they perturb. For this, we will generate chromatin accessibility profiles of astrocytes isolated from MS lesions that we will intersect with MS risk variants. The resulting list of variants and variant-dependent genes will provide a roadmap of astroglial pathways that are dysregulated by MS risk variants and thereby are likely to contribute to astrocyte-mediated MS susceptibility. Our results will help to define the role of astrocytes in genetically mediated MS risk. This will provide a more complete picture of how genetic variants confer susceptibility to MS. Moreover, the epigenomic profiles of astrocytes will be an important resource for research in astrocytes and can be used to investigate genetic dysregulation of astrocytes in other complex genetic disease such as Alzheimer?s disease.